| With the increasing consumption of antibiotics,the antibiotic wastewater generated by the pharmaceutical and livestock has exceeded 250 million tons each year.Because antibiotics have the ability to inhibit or kill microorganisms,antibiotic wastewater is not suitable for conventional biological treatment.In this study,an antibiotic-resistant strain,Stenotrophomonas sp.,was screened from the surface sediment of mangroves forest to prepare immobilized strains to treat COD in high-concentration antibiotic wastewater.In this paper,the magnetic biochar was prepared by co-precipitation-pyrolysis method with bagasse as the precursor.The preparation conditions of the magnetic biochar were optimized by single factor experiments,and the magnetic biochar was characterized by multiple methods.With magnetic biochar as the carrier of the immobilized strains,the conditions of the carrier for immobilizing the strain were optimized by single factor and orthogonal experiments;the removal of COD in simulated wastewater by the immobilized strains was optimized by single factor and orthogonal experiments.The effect of the immobilized strains on the removal of COD in wastewater containing various concentrations of antibiotics under the optimized conditions was investigated.The results of the paper are as follows:(1)Magnetic biochar was prepared by co-precipitation-pyrolysis method,and the preparation conditions were optimized.The optimum pyrolysis temperature for the preparation of magnetic biochar was 500 °C and the pyrolysis time was 4 h.Under this condition,the magnetically modified biochar has a larger surface area(141.62 m2/g),pore volume(0.155 cm3/g)and a higher point of zero charge(p Hpzc=6.56)than the raw biochar,but the pore size decreased and the oxygen content increased.X-ray diffraction,X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analysis showed that the loaded magnetic material was Fe3O4,which showed better magnetic separation performance(saturation magnetization was 23.99 emu/g).(2)Single factor experiments showed that temperature,p H,biochar dosage and time all had a great influence on the ability of magnetic biochar to immobilize strains.The optimal conditions for the immobilization of strains by magnetic biochar were obtained by single factor and orthogonal experiments as follows: temperature 30°C,p H value 8.5,biochar dosage 3 g/L,and immobilization time 20 h.The immobilized biomass was 8.4×1010 CFU/g on this condition.(3)The immobilized strains have a good ability to remove high concentrations of COD in simulated wastewater.The COD removal rate of the immobilized strains in the simulated wastewater reached 54.46% within 48 h(the initial COD concentration was 800 mg/L).The optimized conditions for the removal of COD by the immobilized strains by single factor and orthogonal experiments were as follows: the removal time was 24 h,the temperature was35 °C,the rotational speed was 125 r/min,the p H value was 6.5,and the dosage of immobilized strains was 5 g/L,and the removal rate of COD was 71.3% under this condition.(4)The immobilized strain has a preferable ability to remove COD in antibiotic wastewater.In the presence of a single antibiotic(sulfamethoxazole,penicillin,tetracycline,lincomycin or norfloxacin)at concentrations of 20,50 and100 mg/L,the removal rate of COD by immobilized strains was 1.37%-12.74%higher than that of activated sludge.In the presence of combined antibiotics(sulfamethoxazole + norfloxacin,sulfamethoxazole + tetracycline or norfloxacin+ lincomycin)with total concentrations of 40,100 and 200 mg/L(concentration ratio of 1:1),the removal rate of COD by immobilized strains was 4.12%-30.94%higher than that of activated sludge. |
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